Remote copy which is copying data between first and second storage apparatuses is known. As remote copy, for example, synchronous remote copy and asynchronous remote copy exist. If the first storage apparatus receives a write request from a host and if synchronous remote copy is adopted, a write completion response is transmitted to the host apparatus after data complying with the write request is transferred from the first storage apparatus to the second storage apparatus. Meanwhile, if asynchronous remote copy is adopted, the write completion response is transmitted to the host apparatus even if the data complying with the write request is not transferred from the first storage apparatus to the second storage apparatus.
In a remote copy system to which asynchronous remote copy is adopted (hereinafter referred to as an asynchronous remote copy system), for example, the first storage apparatus comprises a first JVOL (a logical volume in which a journal (hereinafter referred to as a JNL) is stored) as well as a first DVOL (a logical volume in which data is stored). Similarly, the second storage apparatus comprises a second JVOL as well as a second DVOL. If receiving a write request, the first storage apparatus stores data complying with the write request in the first DVOL and, at the same time, stores a JNL including the data in the first JVOL.
The first storage apparatus transfers the JNL in the first JVOL to the second storage apparatus, and the second storage apparatus writes the JNL from the first storage apparatus to the second JVOL. Subsequently, the second storage apparatus writes the data which the JNL in the second JVOL comprises to the second DVOL. By this method, the data written to the first DVOL is considered to have been copied to the second DVOL. As asynchronous remote copy, for example, the technology disclosed in the Patent Literature 1 is known.